Study On The Desalination Process Of Threonine Fermentation Broth

Amino acid is an organic compound containing amino and carboxyl groups.It is widely applied in food,animal husbandry,agriculture and medical health.The most important way to produce amino acids in industry is microbial fermentation.Amino acid fermentation broth has relatively complex ingredients and hence needs to be purified to yield clean amino acid products.This paper mainly studies the desalination of amino acid fermentation broth by electrodialysis(ED).The operating voltages,types of membranes as well as the concentration and pH of the initial feed solution are changed,and ion exchange process is also utilized for desalination of the pretreated threonine(THR)fermentation broth.The ions in the fermentation broth migrate under direct-current electrical field,while the amino acids remain in the fermentation broth.Not only high desalination rate,but also faster desalination speed can be obtained by ED,which can meet the demand of efficiency and speed in industrial process.The full text is composed of five parts,the contents of which are as follows:The first chapter is the introduction,which briefly presents the applications of THR in many fields.The main method of producing THR is microbial fermentation.The components of fermentation broth are complex,and desalination is needed to get high purity THR products.The traditional treatment processes of the fermentation broth are discussed in details,including the principles of each process and the current application fields.At the same time,the feasibility of desalination of the THR fermentation broth is explored.In the second chapter,ED is utilized to remove the inorganic salt ions in the THR fermentation broth.The fermentation broth is complex and needs to be pre-treated by microfiltration and activated carbon decolorization before ED process.The whole pretreatment process could remove 86.8%protein and 88.6%pigment.After pretreatment,the fermentation broth was tested by ED.The effects of working voltage,type of ion exchange membrane,pH and concentration of initial fermentation broth on the results of ED were investigated,and the membrane fouling was also studied.The organic-inorganic hybrid membrane of CEM-412 and AM-QP-30 were loaded into the ED membrane stack.When the working voltage increased from 10 V to 50 V,the desalination time was shortened,the water penetration phenomenon was more obvious,the process energy consumption was increased,and the THR recovery rate was decreased.The study of different types of membranes showed that under 30 V a shorter desalination time(132 min)and a lower process energy consumption(2.996 kW h/kg)were obtained by the hybrid membranes than the commercial membrane,which is related to the hydrophilic PVA-OH group of the hybrid membranes.The third chapter is the adsorption of sulfate in fermentation broth by ion exchange(?),and pretreated macroporous polystyrene chloride anion exchange resin was used.The results showed that with increase of the running time,the resin adsorption capacity of SO42-rose rapidly at first,and then slowly as the adsorption reached saturation.Resin dosage of 1.0 g was more suitable for the removal of SO42-.With the increase of initial SO42-concentration(280-1100 mg/L),the equilibrium adsorption capacity increased gradually(12.44-32.72 mg/g)and SO42-adsorption rate decreased(88.92%-58.95%).The adsorption process of SO42-by ion exchange resin is in accordance with the quasi two stage kinetic model and is mainly the process of chemical adsorption.The isothermal adsorption process for SO42-is in accordance with the Freundlich adsorption isothermal model,and the adsorption and desorption process can be carried out spontaneously.From the IR spectra before and after adsorption of SO42-on chloride resin,it can be seen that the absorption peak of N-Cl bond in-N+(CH3)3Cl-decreased obviously after adsorption,indicating that the resin has completed ion exchange process with SO42-in the fermentation broth.The fourth chapter is about treatment of THR fermentation broth by coupling of ED and IX process,namely,by electrodeionization(EDI)technology so as to further optimize the experimental conditions and solve the shortcomings of the single ED process.The results showed that adding Na,Cl and H,OH ion exchange resin could significantly improve the conductivity of the whole membrane stack,and also reduce the possibility of polarization phenomenon in ED process.The desalination time was shorter and the desalination efficiency was higher than that of the single ED process.At the same time,when the dosage of Na,Cl and H,OH type ion exchange resins was changed,it was found that the efficiency of desalination was proportional to the amount of resin.When different types of ion exchange resin were added to the chamber,the optimal desalting time(123 min)and water recovery rate(85.12%)were obtained by using 5 mL Na and 5 mL Cl resin.It can be seen that the application of EDI technology to the desalination of the THR fermentation broth is favourable,and its stability is superior.The fifth chapter is the summary of the full text.Through the study of various chapters,ED,IX and EDI techniques are feasible for desalination of THR fermentation broth,and good separation effect has been obtained in the laboratory.The results may provide theoretical guidance for the production of fermentation broth and further purification of THR products in industry.